In general, a general multi-touch screen device using infrared light includes receiving and transmitting elements are arranged on the x-axis and the y-axis and measures orthogonal coordinates of touch objects based on whether or not the touch objects block infrared transmitting signals. It uses the receiving and transmitting elements on both the x-axis and the y-axis and is increasingly used.
Infrared signals are AC signals of several tens to hundreds of kHz, and the magnitude of the infrared signals is measured by averaging AC signals collected according to presence and absence of objects blocking infrared light due to touch after radiation. Such a conventional method restricts sensitivity and an overall reaction rate due to lowering of frequency response of infrared light transmitting and receiving elements by time to average the collected AC signals and high-frequency signals.
In the conventional method, since different light sources operated in transmitting units and receiving units interfere with each other, accurate signal reception of receiving elements is not expected and thus, accurate coordinates may not be calculated.
A conventional large infrared touch screen has a difficulty in accurately sensing touch objects and removing ghost images in momentary composite operation in which several persons simultaneously touch the touch screen in several directions.
Further, in the conventional method, infrared signals are radiated so as to be orthogonal between x-axis and y-axis transmitting and receiving units. If multi-touch in a diagonal direction occurs, ghost images may be generated by interaction between a plurality of different touch areas.
FIG. 20 is a view illustrating an infrared type touch screen device disclosed in Korean Patent No. 10-1018397.
In the touch screen device disclosed in Korean Patent No. 10-1018397, in order to remove ghost images, a first scan control mode is performed and then, if multi-touch is sensed, a second scan control mode is separately performed. In the first scan control mode, the case in that actual multi-touch is not recognized as multi-touch is generated and thus, the touch screen device may malfunction. Further, if multi-touch is recognized after the first scan control mode has been performed, an object judged as a ghost image is removed from the multi-touch by separately performing the second scan control mode. Therefore, if movement of multi-touch is frequently carried out, when new multi-touch is generated while performing the second scan control mode, the first scan control mode with respect to the new multi-touch is not operated and the second scan control mode with respect to the former multi-touch is operated and thus, the new multi-touch may not be normally recognized.
Further, in the touch screen device disclosed in Korean Patent No. 10-1018397, transmitting and receiving elements are arranged on both the x-axis and the y-axis, thus requiring a large number of the transmitting and receiving elements.